High intensity discharge (HID) lamps are used in many applications because of their long life and high efficiency. Principal types of HID lamps are high pressure sodium (HPS), pulse start metal halide (PSMH), and mercury vapor lamps.
Mercury vapor, metal halide, and HPS lamps all operate similarly during stabilized lamp operations. The visible light output results from the ionization of gases confined within an envelope and which must be broken down before there is any flow of ionization current. Accordingly, a high open circuit voltage must be applied to an HID lamp for igniting. This voltage is substantially higher than the operating voltage and the available line voltage.
HID lamps also exhibit negative resistance. When operating, their resistance decreases with increase in the applied voltage. As a result, such lamps require an impedance means in their power supply to limit the alternating current flow to a predetermined value.
Because of the high starting or igniting voltage requirement and the negative resistance characteristic, HID lamps are provided with igniting and operating circuits, which provide a relatively high open circuit voltage and impedance means for current limitations. A ballast between the power supply and lamp typically serves as its impedance means in igniting and operating circuits for HID lamps. For HID lamps such as mercury vapor lamps, igniting voltages can be two times the operating voltage. The igniting voltage is generated by the ballast acting in conjunction with a capacitor. For high pressure sodium (HPS) lamps, the required voltages can be more than ten times the operating voltages and more complex igniting mechanisms are employed.
The ballast system also typically provides for certain requirements when electronic ignitors are used in conjunction with the HID lamps. For example, electronic ignitors used in conjunction with high pressure sodium (HPS) ballast coils produce a high voltage pulse to start the HPS lamp. These electronic ignitors work by sensing whether the lamp is burning or not. If the lamp is not burning, the ignitor continuously supplies starting pulses to the lamp, regardless of whether the lamp is not burning because of lamp failure, absence of a lamp in the lamp socket, or by the lamp “cycling off.”
Lamp cycling is a well-known phenomenon in which a lamp nearing the end of its life will light, turn-on for some time, go out, relight, and repeat this cycle time after time until the lamp is replaced or the lamp will fail to start at all. In an HPS lamp, as the HPS lamp nears the end of its life, its lamp operating voltage gets so high that the ballast will no longer sustain operation, and the lamp cycling condition manifests itself.
From the foregoing, it is clear that certain problems can arise in the operation of HID lamps and associated ballasts. In certain situations, e.g., when a lamp is cycling, has failed or is missing, the ignitor in the lamp's HID circuit continues to operate. Such operation shortens ignitor life, especially in cases where the ignitor operates in conjunction with the ballast so that more than normal power is drawn by the ballast transformer. The result of increased current drawn by the ballast transformer can be damaged ballasts by burning or smoking, damaged HID lamp fixtures, and wiring. Cycling lamps can be also avoid replacement by being “on” when inspected and thus cause future maintenance problems.
In view of the above, a number of devices have been developed as ignitor disablers for the starter circuit of a high intensity discharge (HID) lamp. The ignitor disabler circuit typically includes means for disabling the ignitor and means for triggering the disabling means after passage of a predetermined period of time.
U.S. Pat. No. 3,681,653 to Snyder teaches a lighting system for HID lamps for controlling the application of high voltage starting pulses of a capacitor to ignite an HID lamp wherein upon extinguishment of the lamp for any reason a gated bilateral switch is turned off to permit the pulsing circuit to apply a series of high voltage pulses to the lamp to re-ignite the lamp. After the lamp ignites, the circuit does not apply high voltage pulses across either the charging or pulsing capacitor or the switching device, since they are connected on the source sides of the system and not on the lamp side. Upon lamp failure, the charging or pulsing capacitor or switching device being on the source side are not subject to the high voltage pulses, thus prolonging the life of the components.
U.S. Pat. No. 4,258,295 to Siglock discloses a ballast circuit for a sodium vapor lamp wherein the circuit includes a ballast transformer, a high voltage oscillation circuit, and a time delay circuit for delaying the time the lamp starts after the power is turned on. The high voltage oscillation circuit utilizes a capacitor charged to a high potential across a transformer secondary and causes an diac to conduct, getting a triac to cause the triac to discharge the capacitor, to produce a high voltage pulse applied to the lamp to result in sodium ionization of its lamp. Once the sodium arc is formed, the low impedance load causes the voltage to drop to stop operation of the oscillator. A time delay switch circuit triggered by the initial voltage across the transformer primary delays the start-up process of the lamp for a period of time determined by the timer circuit. The time delay switch includes a triac gated by a photodiac triggered by light from a light emitting diode controlled by the timing circuit. A transformer provides power to the timing circuit through a bridge rectifier of four diodes to provide a DC voltage for the timing circuit and a voltage regulator, which may be a commercially available, type 7805 integrated circuit. Timing can be from zero to fifteen minutes based on the RC network connected to the integrated circuit.
U.S. Pat. No. 4,591,781 to Larson discloses a variable control circuit for varying the current to a load and, simultaneously, limiting the output of the load to a predetermined time interval. A timer chip receives rectified current from an AC voltage source. When the output of the timer chip is low at the end of the predetermined time interval, the controlled logic triac controls the flow of current to the load. The timer chip is a commercially available integrated circuit. An RC circuit connected to the timer chip determines the timing output of the chip. A Zener diode, a rectifier diode, series resistors, and a capacitor provide rectified current.
U.S. Pat. No. 4,896,077 to Dodd et al. teaches an ignitor disabler of an HID lamp that disables the ignitor when the characteristic voltage of the lamp exceeds an established AC threshold. The ignitor disabler includes a timing network, which is reset only when an excessive voltage is detected. The reset portion of the disabler includes a field effect transistor for discharging the timing network. The ignitor disabler operates as an HID lamp nears the end of the its life and the lamp operating voltage gets so high that the ballast will no longer sustain operation. The ignitor disabler increases the effective life of ignitors and ballasts.
U.S. Pat. Nos. 4,962,336 and 4,996,464 to Dodd et al. teach ignitor disablers with means for disabling the ignitor and means for triggering the disabling means of the ignitor after passage of a predetermined time. An AC threshold voltage is converted to a DC voltage.
U.S. Pat. No. 5,070,279 to Garbowicz et al. discloses an ignitor circuit for a discharge lamp controlled by a timer to shut off ignitor pulses after a predetermined time if the lamp does not ignite. The timer is controlled by the application of power to the input line and draws power from the output side of the ballast. Output voltage from an opto-isolator is applied to a triac gate when the opto-isolator switch closes. When the triac closes, the ignitor segment of the circuit can function.
U.S. Pat. No. 5,424,617 Garbowicz et al. discloses a ballast for powering a lamp load comprising a power source, an ignition means for generating ignition pulses based on the output voltage, a timing means for controlling when the ignition pulses are to be generated, and voltage sensing means for automatically sensing whenever the output voltage is insufficient for lighting the lamp load. The timing means includes a timing device and an opto-coupler, said opto-coupler being coupled between said timing device and a switching means across the lamp load. The switching means includes a triac having a gate connected to said opto-coupler.
U.S. Pat. No. 5,801,494 to Herres et al. discloses a single, integrated circuit combining both a restrike ignitor and a digital timer circuit, which generates high voltage pulses for starting and restarting high intensity discharge lamps.
U.S. Pat. No. 5,945,784 to Mattas discloses a ballast for an HID lamp, which includes an ignitor and a resonant circuit. The circuit is disabled after a predetermined time following ignition of the lamp.
U.S. Pat. Nos. 6,127,782 and 6,429,597 to Flory, IV et al. disclose an ignitor and ignitor-monitoring device, which is externally mounted to the HID luminaire.
U.S. Pat. No. 6,639,777 to Congdon discloses that timer switches are commonly used to connect the load to the input voltage and suspend the reapplication of power to the load. A timer switch can be used to prevent over-stress to an HID lamp ignitor.
U.S. Pat. No. 6,642,673 to Hudson et al. discloses an ignition disabling circuit wherein a timer circuit generates a timing signal after a selected period of time to disable an ignitor circuit wherein a triac can be opened to cause the ignitor to cease operating.
U.S. Pat. No. 6,731,073 to Van Veldhuizen discloses an automatic starter for fluorescent lamps that includes a timer switch and an electronic timer coupled to the timer switch that prevents the after-glow from continually striking a lamp that has failed. The timer is a solid state timer. The lamp starter circuit incorporates the series arrangement of a glow switch and a semi-conductor switch, the semi-conductor switch being coupled to the solid state timer.
Accordingly, in the prior art, it is known to provide a gated bilateral switch, which is turned off to permit a pulsing circuit to apply high voltage pulses to a lamp to re-ignite an HID lamp using a pulsing capacitor or a switching device on the source side of the system, not on the lamp side. Also, it is known to use a high voltage oscillator to cause a diac to conduct, gating a triac to cause a capacitor to produce a high voltage pulse to an HID lamp. A time delay switch circuit staggers the start-up process of the HID wherein the time delay switch includes a triac gated by a photodiac. A voltage regular circuit comprising an integrated circuit is part of the circuit.
Known circuits in the prior art teach disablers for disabling ignitors in HID lamp monitors. The disablers conventionally are included in the ballast circuiting and the ignitor component as part of the total assembly, the disabler circuitry including a timer and cutoff switch. Known solid state timing devices and circuitry are used in conjunction with gated triacs as control elements as well as opto-couplers and integrated circuitry.